Book selection menu in Tag Browser: Emphasize the books, already having book specific tags

[tklein]

In order to get a better distinction between books, which already have book specific tags and those which don't, there should be a clear visual distinction. Furthermore those books which don't have the tags shouldn't be clickable at all.

[tklein]

(In [169]) fixes #79

• Added method in BibleBook? which finds all bible_books and additionaly loads some meta info
• Use new method BibleBook?.find_all_with_meta_info in bible_book_controller.index
• Add css-classes to each book in book selection menu to find entries easier with JS
• Add context specific book-selection-menu-footer in Tag Browser
• tag_browser_communication_controller - Summarize the following methods in one new method: request_global_tags, request_book_tags, request_bible_book_data => request_tag_data_after_db_change
• Changed book-selection-menu specific classes in main.css